A diver propulsion vehicle (DPV), also known as an underwater propulsion vehicle or underwater scooter, or swimmer delivery vehicle (SDV) by armed forces, is an item of diving equipment used by scuba divers to increase range underwater. Range is restricted by the amount of breathing gas that can be carried, the rate at which that breathing gas is consumed, and the battery power of the DPV. Time limits imposed on the diver by decompression requirements may also limit safe range in practice. DPVs have recreational, scientific and military applications.

DPVs include a range of configurations from small, easily portable scooter units with a small range and low speed, to faired or enclosed units capable of carrying several divers longer distances at higher speeds.

The earliest recorded DPVs were used for military purposes during World War II, and were based on torpedo technology and components.

A DPV usually consists of a pressure-resistant watertight casing containing a battery-powered electric motor, which drives a propeller. The design must ensure that the propeller cannot harm the diver, diving equipment or marine life, the vehicle cannot be accidentally started or run away from the diver, and it remains neutrally buoyant while in use underwater.

DPVs are useful for extending the range of an autonomous diver that is otherwise restricted by the amount of breathing gas that can be carried, the rate at which that breathing gas is consumed, which is increased by exertion, diver fatigue, and the time limits imposed by decompression obligation, which depend on the dive profile.[1] Typical uses include cave diving and technical diving where the vehicles help move bulky equipment and make better use of the limited underwater time imposed by the decompression requirements of deep diving.[2] Military applications include delivery of combat divers and their equipment over distances or at speeds that would be otherwise impracticable. There are accessories that can be mounted to a DPV to make it more useful. Equipment such as lights, compasses, cameras, lobster sticks and even spearguns can also be mounted to DPVs.[citation needed][clarification needed]

DPV operation requires greater situational awareness than simply swimming. Operating a DPV requires simultaneous depth control, buoyancy adjustment, monitoring of breathing gas, and navigation. Buoyancy control is vital for diver safety: The DPV has the capacity to dynamically compensate for poor buoyancy control by thrust vectoring while moving, but on stopping the diver may turn out to be dangerously positively or negatively buoyant if adjustments were not made to suit the changes in depth while moving. If the diver does not control the DPV properly, a rapid ascent or descent under power can result in barotrauma or decompression sickness.[3] High speed travel in confined spaces, or limited visibility can increase the risk of impact with the surroundings at speeds where injury and damage are more likely. Many forms of smaller marine life are very well camouflaged or hide well and are only seen by divers who move very slowly and look carefully. Fast movement and noise can frighten some fish into hiding or swimming away, and the DPV is bulky and affects precise maneuvering at close quarters. The DPV occupies at least one hand while in use and may get in the way while performing precision work like macro photography. Since the diver is not kicking for propulsion, they will generally get colder due to lower physical activity and increased water flow. This can be compensated by appropriate thermal insulation. If the operation of the DPV is critical to exit from a long penetration dive, it is necessary to allow for alternative propulsion in case of a breakdown to ensure safe exit before the breathing gas runs out.

The most common type of DPV tows the diver who holds onto handles on the stern or bow. Tow-behind scooters are most efficient by placing the diver parallel to and above the propeller wash. The diver wears a harness that includes a crotch-strap with a D-ring on the front of the strap. The scooter is rigged with a tow leash that clips to the scooter with releasable metal snap.

These are torpedo or fish-shaped vehicles for one or more divers typically sitting astride them or in hollows inside. The well known human torpedo or chariot was used by commando frogmen in World War II. Similar vehicles have been made for work divers or sport divers but better streamlined as these do not have warheads; the Dolphin made on the Isle of Wight (UK) in the 1971s is an example. Some Farallon and Aquazepp scooters are torpedo-shaped with handles near the bow and a raised seat at the rear to support the diver's crotch against the slipstream. The Russian Protei-5 and Proton carry the diver attached to the top. The New Zealand made Proteus is strapped onto the diver's cylinder.[citation needed]

As DPVs get bigger they gradually merge into submarines. A wet sub is a small submarine where the crew spaces are flooded at ambient pressure and the crew must wear diving gear. Covert military operations use swimmer delivery vehicles (SDVs) to deliver and retrieve operators into harbors and near-shore undetected.[citation needed] An example is the Multi-Role Combatant Craft (MRCC).[4]

These are unpowered boards (usually rectangular) towed by a surface boat which function as diving planes. The diver holds onto the sled and may use a quick-release tether to reduce fatigue. Depth control while submerged is by adjusting the angle of attack. Sometimes known as manta-boards, after the manta ray. Towed sleds are useful for surveys and searches in good visibility in waters where there are not too many large obstacles. The route is largely controlled by the towing vessel, but the diver has a limited amount of control over vertical and lateral excursions.[citation needed]

Divehead 1070 and Divehead 1500[5] are two industrial grade DPVs,[clarification needed] designed and developed by Lian Innovative [6] in China. Divehead is intended to fill the gap between military grade and low-quality recreational DPVs.[clarification needed]

One of the confirmed[by whom?] DPVs in Chinese service are developed by the Kunming Wuwei Science & Technology Trade Co., Ltd[7] at Kunming, a solely owned subsidiary of Kunming 705th (Research) Institute Science & Technology Development Co. (昆明七零五所科技发展总公司))[8] at Kunming, which in turn, is a company wholly owned by the 705th Research Institute (headquartered in Xi'an) of the China Shipbuilding Industry Corporation. A total of 4 DPV models have been identified in Chinese naval service:[verification needed]

In addition to the DPVs currently in the Chinese naval inventory, Glory International Group Ltd[13] in Beijing is also marketing two of its DPVs, (GL602[14] and GL603[15]), to the Chinese military.[verification needed]

Sirena DPV is a Soviet human torpedo around 8 m long with 53 cm diameter so that it can be launched from torpedo tubes. Sirena DPV can transport two divers with a maximum range of 11 nmi at speed of 2-4 kn, with maximum depth of 40 m.[17]

Project 907 Triton 1 is a 1.6 t Soviet DPV manned by 2 crew riding astride spindle-shaped vehicle. The vehicle can rest on the sea bed for up to 10 days before being restarted again thus allowing great operational flexibility. Length is 5 m, beam and draft are both 1.4 m, and maximum depth is 40 m. The vehicle has a maximum range of 35 nmi with 6 hr endurance, and maximum speed is 6 kn.[19]

Project 908 Triton 2 is a 5.3 t Soviet DPV manned capable of carrying 6 crew. Although a wet sub, the design incorporates a system to maintain a constant pressure within the submarine regardless of depth. Length is 9.5 m, beam is 2.0 m and draft is 2.2 m, and maximum depth is 40 m. The vehicle has a maximum range of 60 nmi with 12 hr endurance, and maximum speed is 6 kn.[19]

2 men crew SDV with 30+ kn on surface and can be parked on the sea floor. There are three different modules for the Carrier providing different applications including: SEAL SDV – Swimmer Delivery Vehicle for SOP missions, SEAL AUV – Autonomous Under- water Vehicle for MCM missions, and SEAL RWSV – Remote Weapon Station Vehicle for Fire Support.[23]

Smart SEAL

A downsized SEAL Carrier, with 30+ kn on surface and can be parked on the sea floor.[24]

After purchasing US submersible manufacturer Seahorse Marine, Emirate Marine Technologies of United Arab Emirates has developed four classes DPV/SDV, all of them built of glass reinforced plastic and carbon composite materials:

Class 4

Three-ton two-man DPV using silver-zinc external battery packs to power an 8 kW motor. Sensor and control suites include a sonar, echo sounder, GPS, electronic compass and electronic mapping facility and an onboard computer. They have a range of 60 nmi (110 km) at 6 (maximum speed 7) kn and can operate down to 50 m. Maximum payload is 200 kg.[28]

Class 5

Eight-ton two-man DPV using nickel-cadmium external battery packs to power an 8 kW motor. All other specs are identical to Class 4 except the maximum payload is increased to 450 kg.[28]

Class 6

DPV/SDV currently under development to carry 4 or 8 (2 crew) divers. Will have 2 8 kW motors for underwater use and a diesel for surface operations. There will be computer-controlled system--including an automatic pilot to reduce operator workload, and a telescopic mast with a television camera and/or a thermal imager. Class 6 will have a range of 100 nmi (185 km) at 4 knots down to 50 m, but on the surface the diesel will give it a maximum speed of 20 kn. There will be built-in breathing sets for divers to conserve their underwater breathing apparatuses.[28]

Class 8

11 m long DPV/SDV propelled by two eight-kW motors and powered by a lithium-ion battery for 6 divers (2 crew) currently under development. Maximum range is 50 nmi (93 km) at 5 kn with a maximum speed of 6 kn.[28]

1.63 t two-man DPV/SDV developed by Columbia Research Corporation built of fiber-glass. Maximum range is 27.5 nmi @ 5 kn but burst speed of 8 kn can be achieved with its powerful brush-less DC motor and silver-zinc batteries. Maximum depth is 70 m, although it will usually be kept around 45 m.[29]

2.75 t 6 to 8-man DPV/SDV developed by Columbia Research Corporation built of fiber-glass. Maximum range is 56.5 nmi (104.5 km) @ 5 kn but burst speed of 8 kn can be achieved with its powerful brush-less DC motor and silver-zinc batteries. Maximum depth is 91 m, although it will usually be kept around 45 m.[29] Electronics include color liquid crystal displays and color digital charts, while the computer-based navigation system includes GPS and Doppler velocity log. There is also a multi-beam obstacle-avoidance sonar to distinguish targets while the integrated communications suite includes an underwater telephone and a VHF radio.[28]

Developed by Anteon Corp, a wholly owned subsidiary of General Dynamics since 2006, the 107 kg Sea Shadow is for one or two crew and powered by lead-acid batteries. The hull is of molded high-density polyethylene plastic to provide a low magnetic signature while folding bow planes and rotating motors allow the vehicle to be deployed through a 76-cm escape hatch. The Sea Shadow features electronic speed control with a manual back-up mode and an option of electronic drift compensation. Speed, depth, battery duration and voltage details is shown on a liquid crystal display, while there are visual warning signals on low battery power as well as unsafe rates of both ascent and descent. Sea Shadow has a range of 5 nmi (9.25 km) at 2 to 3 kn and at a maximum of depth of 30 m.[28]

All SDVs of former Yugoslavia were developed by Brodosplit - Brodogradilište Specijalnih Objekata d.o.o. which have been passed on to successor nations of former Yugoslavia.

R-1

150 kg one-man torpedo like SDV with the operator straddling the aluminium alloy hull behind the first of two buoyancy tanks, and the operator can deliver 40 kg of limpet mines of either the 7 or 15 kg size. This SDV has a dimension of 3.72 meter (length) x 0.52 m (diameter) and can be housed in a submarine torpedo tube. The silver-zinc batteries operating a one-kW motor with a range of 8 kn (15 km) at 2.5 kn (maximum speed 3 kn) at a maximum depth of 60 m.[28]

1.41 t two-man SDV with crew ride astride spindle-shaped vehicle. The 4.5 kW DC electric motor is powered by either lead-acid or silver-zinc batteries, providing a maximum range of 23 nmi or 46 nmi. The cruise and maximum speed are 2.8 and 6.5 kn. Navigation equipment comprises an aircraft-type gyro compass, a magnetic compass, depth gauge with a 0 to 100-metre scale, echo-sounder, sonar, two searchlights and so on, all of which equipment is in a waterproof container. The R-2 can operate down to 60 meters with a maximum depth of 100m and a maximum limpet mine load of 250 kg.[28]

Human torpedoes or manned torpedoes are a type of diver propulsion vehicle used as secret naval weapons in World War II. The name was commonly used to refer to the weapons that Italy, and later Britain, deployed in the Mediterranean and used to attack ships in enemy harbours. The first human torpedo was the Italian Maiale ("Pig"). In operation, it was carried by another vessel (usually a normal submarine), and launched near the target. It was electrically propelled, with two crewmen in diving suits and rebreathers riding astride. They steered the torpedo at slow speed to the target, used the detachable warhead as a limpet mine and then rode the torpedo away.[citation needed]

The idea was successfully applied by the Italian navy (Regia Marina) early in World War II and then copied by the British when they discovered how effective this weapon could be was after three Italian unitss successfully penetrated the harbour of Alexandria and damaged the two British battleships HMS Queen Elizabeth and HMS Valiant, and the tanker "Sagona." The official Italian name for their craft was "Siluro a Lenta Corsa" (SLC or "Slow-running torpedo"), but the Italian operators nicknamed it "Maiale" after their inventor Teseo Tesei angrily called it a pig when it had been difficult to steer. The British copies were named "chariots".[citation needed]